It is well known to support a shaft using a split bearing support having two parts defining a bore in which is rotatably supported the shaft.
The assembly of rotating shafts requires split bearing supports with bores that provide very good positional tolerance, cylindricity and concentricity irrespective of the type of bearing used.
The required accuracy is best met if the split bearing supports are line bored together, that is to say, all concentric bores are machined in one operation with all parts in position.
In order to meet functional requirements, it is important that the bearing caps that form one half of the split bearing supports are re-assembled exactly in the same position during engine assembly or during any subsequent engine servicing.
Various methods have previously been used to ensure each bearing cap goes back in its original position during assembly but these methods do not necessarily prevent mistakes occurring during assembly of the bearing caps. For example, markings can be applied to each bearing cap by printing, engraving or casting to help the assembly operator to replace the bearing caps correctly.
Such markings have a number of disadvantages, for example, printed or engraved markings lead to increased piece price and cast marking fades and becomes less legible as the casting tool wears out.
For all markings, they provide guidance to the operator but do not prevent mistakes in assembly as the bearing caps can still be assembled the wrong way round or in the wrong position.
In order to try to overcome such problems it is known from U.S. Pat. No. 4,854,746 to provide a bearing cap that is flanked by first and second shoulders which are asymmetrical in shape and so prevent the bearing cap being wrongly positioned in a recess defined by precision machined guide surfaces formed in a bearing support member when a shaft to be supported is in position.
Although such an arrangement solves some of the problems associated with marking of the bearing caps it is only appropriate where a precision machined recess is formed in the bearing support member. The production of such a precision machined surface is expensive and time consuming to produce.
It is an object of the invention to provide a bearing cap that is simple and cost effective to produce but is so configured as to prevent the bearing cap from being assembled in an incorrect orientation.
It is a further object of the invention to provide a shaft assembly having two or more bearing caps that cannot be assembled in the wrong position.
According to a first aspect of the invention there is provided a shaft assembly comprising a shaft rotatably supported for rotation about an axis of rotation by at least two bearing support assemblies, each bearing support assembly comprising a bearing support structure defining first and second reference bores and a first semi-cylindrical recess having a central axis, each bearing support assembly further comprising a bearing cap having first and second feet joined by a bridge portion that defines a second semi-cylindrical recess for supporting the shaft, the first foot of the bearing cap having a first reference bore formed therein for accommodating in use a first location dowel and the second foot of the bearing cap having a second reference bore formed therein for accommodating in use a second location dowel, the first reference bore of the bearing cap being offset from a central axis of the second semi-cylindrical recess by a first distance and the second reference bore of the bearing cap being offset from the central axis of the second semi-cylindrical recess by a second distance that is different to the first distance, each bearing cap being fastened to the bearing support structure by a pair of bolts and by the first and second location dowels engaged with the first and second reference bores in the bearing support structure and the first and second reference bores in the bearing cap so as to align the two reference bores in the bearing support structure with the two reference bores in the bearing cap so that, in use, the central axes of the first and second semi-cylindrical recesses in the bearing support structure and the attached bearing cap are both coaxially aligned with the axis of rotation of the shaft, wherein each bearing support assembly has a centre spacing between the aligned reference bores that is different to the centre spacing of any other bearing support assembly used to support the shaft.
The first foot of each bearing cap may have a first clearance bolt hole extending therethrough for accommodating a first bolt used to secure the bearing cap in use to a corresponding bearing support structure and the second foot of each bearing cap may have a second clearance bolt hole extending therethrough for accommodating a second bolt used to secure the bearing cap in use to the bearing support structure, the first reference bore of each bearing cap may be formed in a mating face of the first foot that abuts in use against a first complementary face on the bearing support structure and the second reference bore of each bearing cap may be formed in a mating face of the second foot that abuts in use against a second complementary face on the bearing support structure.
The first reference bore of each bearing cap and the first clearance bolt hole of each bearing cap may be coaxially aligned and the second reference bore of each bearing cap and second clearance bolt hole of each bearing cap may be coaxially aligned.
For each bearing cap, the mating face of the first foot and the mating face of the second foot may both lie on a common plane and the first and second distances may be measurements from the central axis of the second semi-cylindrical recess along the common plane.
For each bearing cap, the first distance may be a measurement of the distance of a central axis of the first reference bore of the bearing cap from the central axis of the second semi-cylindrical recess and the second distance may be a measurement of the distance of a central axis of the second reference bore of the bearing cap from the central axis of the second semi-cylindrical recess.
The semi-cylindrical recesses of the bearing support structure and the bearing cap of each bearing support assembly may co-operate in use to support a bearing for the shaft.
The bearing may be one of a roller bearing, a ball bearing and a plain bearing. Each bearing support structure may be formed as part of a structural part of an engine.
The first foot of each bearing cap may have first and second clearance bolt holes extending therethrough for accommodating first and second bolts used to secure the bearing cap in use to the bearing support structure, and the second foot of each bearing cap may have third and fourth clearance bolt holes extending therethrough for accommodating third and fourth bolts used to secure the bearing cap in use to the bearing support structure.
The first and second clearance bolt holes may be offset from the first reference bore of the first foot of the bearing cap, and the third and fourth clearance bolt holes may be offset from the second reference bore of the second foot of the bearing cap.
According to a second aspect of the invention there is provided an engine having at least one shaft assembly constructed in accordance with said first aspect of the invention. The engine may further comprise a cylinder block and a ladderframe bolted to a lower end of the cylinder block, wherein the ladderframe defines a bearing support structure of each bearing support assembly.
The shaft may be one of a crankshaft, a camshaft and a balancer shaft of the engine. The shaft assembly may have exactly one shaft, and each bearing cap may have exactly one semi-circular recess for supporting the one shaft. Further, each bearing cap may have exactly two feet.
According to a third aspect of the invention there is provided a method of producing a shaft assembly constructed in accordance with said first aspect of the invention, the method comprising manufacturing a shaft, manufacturing a component having at least two bearing support structures each of which has a semi-circular recess and first and second reference bores and two or more threaded bores, manufacturing a like number of bearing caps as there are bearing support structures, each of the bearing caps having a semi-circular recess, first and second reference bores, and two or more bolt clearance holes, wherein the method further comprises machining the two reference bores in each bearing cap so that the first reference bore is offset from a central axis of the respective semi-cylindrical recess by a first distance and the second reference bore is offset from the central axis of the respective semi-cylindrical recess by a second distance that is different than the first distance, machining the two reference bores in each bearing support structure to match the spacing of the first and second reference bores in the respective bearing cap to which it is secured in use, fitting dowels in the first and second reference bores in the bearing support structures and the bearing caps, aligning and bringing into mating contact each bearing cap with the respective bearing support structure so as to produce full engagement of the dowels with the first and second reference bores in the bearing caps and bearing support structures, securing the bearing caps to the bearing support structures, and simultaneously line boring the semi-cylindrical recesses in the bearing support structures and bearing caps to produce a bore of a required diameter.
The method may further comprise removing the bearing caps from the bearing support structures after the line boring is complete, placing the shaft and associated bearings in position, replacing the bearing caps on the matching bearing support structures, and bolting the bearing caps to the bearing support structures.
Before the line boring, the semi-cylindrical recesses of the bearing support structures and bearing caps may each have a first diameter, whereas after the line boring, the semi-cylindrical recesses of the bearing support structures and bearing caps may each have a second diameter larger than the first diameter.
Machining each reference bore of the bearing support structures may comprise machining a chamfered lead-in at a mounting face end thereof, and machining each reference bore of the bearing caps may comprise machining a chamfered lead-in at a mounting face end thereof. Further, the dowels may comprise chamfers.
Each bearing cap may further comprise first and second bolt clearance holes in a first foot thereof and third and fourth bolt clearance holes in a second foot thereof. In such examples, machining the first and second reference bores in each bearing cap may comprise machining the first reference bore at an offset from each of the first and second bolt clearance holes and machining the second reference bore at an offset from each of the third and fourth bolt clearance holes.